This project will provide new information on the catalytic properties of the proteolytic enzyme of the Human Immunodifficiency Virus, HIV-PR. This is an essential catalytic activity for the replication and maturation of infectious virus particles and is a target for antiviral therapy. We will prepare a series of oligopeptide substrates designed to test several theories of substrate structure and active site properties. The two main new proposals are that the substrate must exist in either a) a beta turn conformation at the cleavage point, or b) a two-stranded beta sheet dimer in order for productive enzyme-substrate interaction to occur. These theories are derived from the observations that, although simple linear oligopeptides are cleaved by the isolated enzyme, the observed kinetic parameters are anemic at best. We will design constrained peptides by placing Cys residues at specific points to favor formation of either a cis or trans Tyr-Pro peptide bond in a cyclic, disulfide linked peptide. To test the alternate theory of dimer formation, we will construct parallel as Well as anti-parallel dimers by strategic location of Cys and Lys residues. In both cases, construction of a conformation that resembles the native structure in the viral polyprotein should lead to greatly enhanced binding or catalytic properties. Finally, we will build upon this new information to include chromophoric groups in an effort to produce a continuous spectrophotometric assay for this important enzyme. This assay would be extremely valuable for characterization of potential anti- viral inhibitors.